THE ORIGIN AND KINETICS OF MONONUCLEAR PHAGOCYTES

The origin and turnover of efferent populations of mouse mononuclear phagocytes has been described. Mononuclear phagocytes were defined as mononuclear cells which are able to adhere to glass and phagocytize. In vitro labeling studies with thymidine-³H showed that monocytes in the peripheral blood and peritoneal macrophages do not multiply and can be considered end cells in a normal, steady state situation. However, the mononuclear phagocytes of the bone marrow appear to be rapidly dividing cells. This conclusion was supported by in vivo labeling experiments. A peak of labeled mononuclear phagocytes of the bone marrow was found 24 hr after a pulse of thymidine-³H. This was followed, 24 hr later, by a peak of labeled monocytes in the peripheral blood. From these experiments it was concluded that the rapidly dividing mononuclear phagocytes of the bone marrow, called promonocytes, are the progenitor cells of the monocytes. Labeling studies after splenectomy and after X-irradiation excluded other organs as a major source of the monocytes. Peak labeling of both the blood monocyte and peritoneal macrophages occurred at the same time. A rapid entry of monocytes from the blood into the peritoneal cavity was observed, after a sterile inflammation was evoked by an injection of newborn calf serum. These data have led to the conclusion that monocytes give rise to peritoneal macrophages. No indications have been obtained that mononuclear phagocytes originate from lymphocytes. In the normal steady state the monocytes leave the circulation by a random process, with a half-time of 22 hr. The average blood transit time of the monocytes has been calculated to be 32 hr. The turnover rate of peritoneal macrophages was low and estimated at about 0.1% per hour. On the basis of these studies the life history of mouse mononuclear phagocytes was formulated to be: promonocytes in the bone marrow, → monocytes in the peripheral blood, → macrophages in the tissue.     

The healing myocardium sequentially mobilizes two monocyte subsets with divergent and complementary functions

Healing of myocardial infarction (MI) requires monocytes/macrophages. These mononuclear phagocytes likely degrade released macromolecules and aid in scavenging of dead cardiomyocytes, while mediating aspects of granulation tissue formation and remodeling. The mechanisms that orchestrate such divergent functions remain unknown. In view of the heightened appreciation of the heterogeneity of circulating monocytes, we investigated whether distinct monocyte subsets contribute in specific ways to myocardial ischemic injury in mouse MI. We identify two distinct phases of monocyte participation after MI and propose a model that reconciles the divergent properties of these cells in healing. Infarcted hearts modulate their chemokine expression profile over time, and they sequentially and actively recruit Ly-6C^hi and -6C^lo monocytes via CCR2 and CX₃CR1, respectively. Ly-6C^hi monocytes dominate early (phase I) and exhibit phagocytic, proteolytic, and inflammatory functions. Ly-6C^lo monocytes dominate later (phase II), have attenuated inflammatory properties, and express vascular–endothelial growth factor. Consequently, Ly-6C^hi monocytes digest damaged tissue, whereas Ly-6C^lo monocytes promote healing via myofibroblast accumulation, angiogenesis, and deposition of collagen. MI in atherosclerotic mice with chronic Ly-6C^hi monocytosis results in impaired healing, underscoring the need for a balanced and coordinated response. These observations provide novel mechanistic insights into the cellular and molecular events that regulate the response to ischemic injury and identify new therapeutic targets that can influence healing and ventricular remodeling after MI.     

THE PRESENCE OF PLASMA INHIBITORS DURING THE CRISIS PHENOMENON IN EXPERIMENTAL RELAPSING FEVER (BORRELIA NOVYI)

The intensity and duration of Borrelia novyi infection in rats depends upon the dose of spirochetes administered. The spirochetemia in response to an inoculum of 1 x 10⁸ spirochetes/kg. characteristically reaches a peak of 4 to 5 million organisms per c.mm. of blood at about 72 hours. Resolution of the primary infection occurs within 48 hours after the peak counts have been observed, with crisis ending at 100 to 120 hours after inoculation. Treatment of the acute infection, so standardized, by 10 ml./kg. of crisis plasma intraperitoneally delays the onset of the spirochetemia 76 to 140 hours, and reduces the maximal spirochetal count 10^–3 to 10^–6 that of the unmodified controls. This is evidence that inhibitor is present in the plasma at the time of crisis and plays a role in limiting the primary infection and subsequent relapses. The activity of crisis plasma is not destroyed by freezing, or after storage at 4°C. for 4 days. Fractions I + II + III and IV + V+ VI from crisis plasma, obtained by method 10 of Cohn et al., were also effective in suppressing the acute spirochetemia, but differed in duration and effectiveness. The first of these was about as potent as the undiluted whole plasma, and the second about as potent as plasma diluted 1:4.     

An adventitial IL-6/MCP1 amplification loop accelerates macrophage-mediated vascular inflammation leading to aortic dissection in mice

Vascular inflammation contributes to cardiovascular diseases such as aortic aneurysm and dissection. However, the precise inflammatory pathways involved have not been clearly defined. We have shown here that subcutaneous infusion of Ang II, a vasopressor known to promote vascular inflammation, into older C57BL/6J mice induced aortic production of the proinflammatory cytokine IL-6 and the monocyte chemoattractant MCP-1. Production of these factors occurred predominantly in the tunica adventitia, along with macrophage recruitment, adventitial expansion, and development of thoracic and suprarenal aortic dissections. In contrast, a reduced incidence of dissections was observed after Ang II infusion into mice lacking either IL-6 or the MCP-1 receptor CCR2. Further analysis revealed that Ang II induced CCR2⁺CD14^hiCD11b^hiF4/80^– macrophage accumulation selectively in aortic dissections and not in aortas from Il6^–/– mice. Adoptive transfer of Ccr2^+/+ monocytes into Ccr2^–/– mice resulted in selective monocyte uptake into the ascending and suprarenal aorta in regions of enhanced ROS stress, with restoration of IL-6 secretion and increased incidence of dissection. In vitro, coculture of monocytes and aortic adventitial fibroblasts produced MCP-1– and IL-6–enriched conditioned medium that promoted differentiation of monocytes into macrophages, induced CD14 and CD11b upregulation, and induced MCP-1 and MMP-9 expression. These results suggest that leukocyte-fibroblast interactions in the aortic adventitia potentiate IL-6 production, inducing local monocyte recruitment and activation, thereby promoting MCP-1 secretion, vascular inflammation, ECM remodeling, and aortic destabilization.     

THE YIELD OF RABIES VIRUS IN THE CHICK EMBRYO

Rabies virus was inoculated intracerebrally in 8 day old chick embryos and the virus activity of pools of embryos titered after incubation at 35–36°C. for different lengths of time. The virus reached a titer of 10^–5.5 to 10^–6.5 in 5 to to 6 days and remained at a rather constant level until the 9th day of the infection. The report by Kligler and Bernkopf that rabies virus will invade the very young embryo after inoculation on the chorioallantoic membrane was confirmed.     

A new approach for diagnosing chronic myelomonocytic leukemia using structural parameters of Sysmex XNTM analyzers in routine laboratory practice

According to WHO recommendations, diagnosis of chronic myelomonocytic leukemia (CMML) beforehand requires microscopic examination of peripheral blood to identify dysplasia and/or blasts when monocytes are greater or equal to 1.0?×?10⁹/L and 10% of leucocytes. We analyzed parameters derived from Sysmex^TM XN analyzers to improve the management of microscopic examination for monocytosis. We analyzed results of the complete blood count and the positioning and dispersion parameters of polymorphonuclear neutrophils and monocytes in 61 patients presenting with CMML and 635 control patients presenting with a reactive monocytosis. We used logistic regression and multivariate analysis to define a score for smear review. Three parameters were selected: neutrophil/monocyte ratio, structural neutrophil dispersion (Ne-WX) and monocyte absolute value. We established an equation in which the threshold of 0.160 guided microscopic examination in the search for CMML abnormalities with a sensitivity of 0.967 and a specificity of 0.978 in the learning cohort (696 samples) and 0.923 and 0.936 in the validation cohort (1809 samples) respectively. We created a score for microscopic smear examination of patients presenting with a monocytosis greater or equal to 1.0?×?10⁹/L and 10% of leucocytes, improving efficiency in laboratory routine practice.     

Transforming Growth Factor β1, in the Presence of Granulocyte/Macrophage Colony-stimulating Factor and Interleukin 4, Induces Differentiation of Human Peripheral Blood Monocytes into Dendritic Langerhans Cells

Langerhans cells (LCs) are dendritic cells (DCs) that are present in the epidermis, bronchi, and mucosae. Although LCs originate in bone marrow, little is known about their lineage of origin. In this study, we demonstrate that in vitro LCs may originate from monocytes. Adult peripheral blood CD14⁺ monocytes differentiate into LCs (CD1a⁺, E-cadherin⁺, cutaneous lymphocyte-associated antigen⁺, Birbeck granules⁺, Lag⁺) in the presence of granulocyte/macrophage colony-stimulating factor, interleukin 4, and transforming growth factor β1 (TGF-β1). This process occurs with virtually no cell proliferation and is not impaired by 30 Gy irradiation. Selection of monocyte subpopulations is ruled out since monocyte-derived DCs can further differentiate into LCs. Our data suggest that in vivo LC differentiation may be induced peripherally, from a nonproliferating myeloid precursor, i.e., the monocyte, in response to a TGF-β1–rich microenvironment, as found in the skin and epithelia. Therefore, the monocyte may represent a circulating precursor critical to the immune response in vivo.     

Monocyte Selectivity and Tissue Localization Suggests a Role for Breast and Kidney–Expressed Chemokine (Brak) in Macrophage Development

Although numerous chemokines act on monocytes, none of them is specific for these cells. Here, we show that breast and kidney–expressed chemokine (BRAK) is a highly selective monocyte chemoattractant. Migration efficacy and Bordetella pertussis toxin–sensitive Ca²⁺ mobilization responses to BRAK were strongly enhanced after treatment of monocytes with the cyclic AMP–elevating agents prostaglandin E₂ and forskolin. BRAK is the first monocyte-selective chemokine, as other types of blood leukocytes or monocyte-derived dendritic cells and macrophages did not respond. Expression in normal skin keratinocytes and dermal fibroblasts as well as lamina propria cells in normal intestinal tissues suggests a homeostatic rather than an inflammatory function for this chemokine. In addition, macrophages were frequently found to colocalize with BRAK-producing fibroblasts. We propose that BRAK is involved in the generation of tissue macrophages by recruiting extravasated precursors to fibroblasts, which are known to secrete essential cytokines for macrophage development.     

The role of the donor group and electron-accepting substitutions inserted in π-linkers in tuning the optoelectronic properties of D–π–A dye-sensitized solar cells: a DFT/TDDFT study

The design of low-cost and high-efficiency sensitizers is one of the most important factors in the expansion of dye-sensitized solar cells (DSSCs). To obtain effective sensitizer dyes for applications in dye-sensitized solar cells, a series of metal-free organic dyes with the D–π–A–A arrangement and with different donor and acceptor groups have been designed by using computational methodologies based on density functional theory (DFT) and time-dependent density functional theory (TD-DFT). We have designed JK-POZ(1–3) and JK-PTZ(1–3) D–π–A–A organic dyes by modifying the donor and π-linker units of the JK-201 reference dye. Computational calculations of the structural, photochemical properties and electrochemical properties, as well as the key parameters related to the short-circuit current density and open-circuit voltage, including light-harvesting efficiency (LHE), singlet excited state lifetime (τ), reorganization energies (λ_total), electronic injection-free energy (ΔG^inject) and regeneration driving forces (ΔG^reg) of dyes were calculated and analyzed. Moreover, charge transfer parameters, such as the amount of charge transfer (q^CT), the charge transfer distance (D^CT), and dipole moment changes (μ^CT), were investigated. The results show that ΔG^reg, λ_max, λ_total and τ of JK-POZ-3 and JK-PTZ-3 dyes are superior to those of JK-201, indicating that novel JK-POZ-3 and JK-PTZ-3 dyes could be promising candidates for improving the efficiency of the DSSCs devices.

A series of metal-free organic dyes with the D–π–A–A arrangement and with different donor and acceptor groups have been designed theoretically.     

Validation of ‘lock-and-key’ mechanism of a metal–organic framework in selective sensing of triethylamine

To develop the metal–organic framework (MOF)-based sensing of triethylamine (TEA) in an aqueous phase, Al-MIL-101-NH₂ (MIL: Material Institute Lavoisier) with a tripod-like cavity was utilized based on a lock-and-key model. Al-MIL-101-NH₂ (Al-MOF) was found to be an excellent fluorescent sensor for the TEA molecules in the range of 0.05–0.99 mM. The limit of detection (LOD) and linear calibration range of this probe towards TEA were found to be 3 μM and 0.05–0.40 mM, respectively. The mechanism of the sensing process indicates the dominant role of physical processes (e.g., non-covalent bond interactions). In addition, the exact fit of the TEA molecule (6.5 Å) in the tripod-like cavity (6.78 Å) supported the strong interaction between three ethyl groups (TEA) and aromatic rings (MOF). This kind of specific suitability between size/shape of the TEA and tripod-like cavity of MOF (ΔG: −46.7 kJ mol⁻¹) was not found in other molecules such as ethylamine (ΔG: −2.20 kJ mol⁻¹ and size: 3.7 Å), formaldehyde (ΔG: +1.50 kJ mol⁻¹ and size: 2.8 Å), and ammonia (ΔG: +0.71 kJ mol⁻¹ and size: 1.6 Å). As such, Al-MOF was found to be a selective and stable sensor for TEA.

To develop the metal–organic framework (MOF)-based sensing of triethylamine (TEA) in an aqueous phase, Al-MIL-101-NH₂ (MIL: Material Institute Lavoisier) with a tripod-like cavity was utilized based on a lock-and-key model.     

Gadolinium-conjugated star-block copolymer polylysine-modified polyethylenimine as high-performance T1 MR imaging blood pool contrast agents

Core–shell copolymers have received widespread attention because of their unique properties, such as suitable for surface modification and increasing the functionality. Thus, they have been increasingly used in many fields including biomedical, pharmaceutical, electronics and optics. Here, a new core–shell copolymer system was developed to synthesize potential blood pool contrast agent (CA) for magnetic resonance imaging (MRI). The novel CA with high T₁ relaxivity was synthesized by conjugating gadolinium (Gd) chelators onto star-block copolymer polyethylenimine-grafted poly(l-lysine) (PEI–PLL) nanoparticles (NPs). The T₁ relaxivity of PEI–PLL–DTPA–Gd NPs measured on a 7.0 T small animal MRI scanner was 8.289 mM⁻¹ s⁻¹, higher than that of T₁ contrast agents widely used in the clinic, such as Gd–DTPA (also known as Magnevist, r₁ = 4.273 mM⁻¹ s⁻¹). These results show that PEI–PLL–DTPA–Gd exhibits more efficient T₁ MR contrast enhancement compared to Gd–DTPA. More importantly, the PEI–PLL–DTPA–Gd core–shell NPs exhibited extremely low toxicity when measured against the HepG2 cell line over a similar concentration rang of Magnevist. In in vivo experiments, PEI–PLL–DTPA–Gd not only displayed good T₁ contrast enhancement for the abdominal aorta, but also showed prolonged blood circulation time compared with Gd–DTPA, which should enable longer acquisition time, for MR and MR angiographic images, with high resolution in clinical practice. PEI–PLL–DTPA–Gd NPs have potential to serve as high T₁ relaxivity blood pool MRI CA in the clinic.

Core–shell copolymers have received widespread attention because of their unique properties, such as suitable for surface modification and increasing the functionality.     

STUDIES IN THE BLOOD CYTOLOGY OF THE RABBIT : V. CONSECUTIVE LYMPHOCYTE AND MONOCYTE OBSERVATIONS ON GROUPS OF NORMAL RABBITS

Consecutive weekly observations on the lymphocyte and monocyte counts of the peripheral blood were made on 5 groups of normal rabbits, a total of 45 animals, during a period of 20 months from October, 1927 to July, 1929. Individual groups were examined 8 to 35 weeks. The results are analyzed on the basis of the mean group values of each week. In the case of the 4 groups followed 13 to 35 weeks, there was a general tendency for the lymphocyte mean values to become increased; with the group observed 8 weeks, the level of mean values showed little change. The general trend of the monocyte mean values was also in the direction of higher levels but it was less pronounced than that of the lymphocytes. The period of greatest irregularity in the mean values of the lymphocytes was in the late winter and spring months of both years. With the monocytes, periods of fluctuating values occurred in the fall of 1927, the spring and early summer of 1928, and in the late winter, spring, and early summer of 1929. There was a certain degree of parallelism in the case of two groups examined during the same months with respect to the direction and time of occurrence of a change in the level of lymphocyte and monocyte mean values. The general levels of lymphocyte and monocyte mean values in the groups examined during 1927–28 were higher than in the groups of 1928–29. The results based upon the trends of mean group values obtained from consecutive weekly observations showed no evidence of a consistent numerical relationship between lymphocytes and monocytes.     

TREM-1 orchestrates angiotensin II–induced monocyte trafficking and promotes experimental abdominal aortic aneurysm

The triggering receptor expressed on myeloid cells 1 (TREM-1) drives inflammatory responses in several cardiovascular diseases but its role in abdominal aortic aneurysm (AAA) remains unknown. Our objective was to explore the role of TREM-1 in a mouse model of angiotensin II–induced (AngII–induced) AAA. TREM-1 expression was detected in mouse aortic aneurysm and colocalized with macrophages. Trem1 gene deletion (Apoe^–/–Trem1^–/–), as well as TREM-1 pharmacological blockade with LR-12 peptide, limited both AAA development and severity. Trem1 gene deletion attenuated the inflammatory response in the aorta, with a reduction of Il1b, Tnfa, Mmp2, and Mmp9 mRNA expression, and led to a decreased macrophage content due to a reduction of Ly6C^hi classical monocyte trafficking. Conversely, antibody-mediated TREM-1 stimulation exacerbated Ly6C^hi monocyte aorta infiltration after AngII infusion through CD62L upregulation and promoted proinflammatory signature in the aorta, resulting in worsening AAA severity. AngII infusion stimulated TREM-1 expression and activation on Ly6C^hi monocytes through AngII receptor type I (AT₁R). In human AAA, TREM-1 was detected and TREM1 mRNA expression correlated with SELL mRNA expression. Finally, circulating levels of sTREM-1 were increased in patients with AAA when compared with patients without AAA. In conclusion, TREM-1 is involved in AAA pathophysiology and may represent a promising therapeutic target in humans.     

P-Stereodefined phosphorothioate analogs of glycol nucleic acids—synthesis and structural properties

Enantiomerically pure, protected acyclic nucleosides of the GNA type (glycol nucleic acids) (^GN′), obtained from (R)-(+)- and (S)-(−)-glycidols and the four canonical DNA nucleobases (Ade, Cyt, Gua and Thy), were transformed into 3′-O-DMT-protected 2-thio-4,4-pentamethylene-1,3,2-oxathiaphospholane derivatives (OTP-^GN′) containing a second stereogenic center at the phosphorus atom. These monomers were chromatographically separated into P-diastereoisomers, which were further used for the synthesis of P-stereodefined “dinucleoside” phosphorothioates ^GN_PST (^GN = ^GA, ^GC, ^GG, ^GT). The absolute configuration at the phosphorus atom for all eight ^GN_PST was established enzymatically and verified chemically, and correlated with chromatographic mobility of the OTP-^GN′ monomers on silica gel. The ^GN_PS units (derived from (R)-(+)-glycidol) were introduced into self-complementary PS-(DNA/GNA) octamers of preselected, uniform absolute configuration at P-atoms. Thermal dissociation experiments showed that the thermodynamic stability of the duplexes depends on the stereochemistry of the phosphorus centers and relative arrangement of the ^GN units in the oligonucleotide strands. These results correlate with the changes of conformation assessed from circular dichroism spectra.

The stability of P-stereodefined PS-(DNA/GNA) duplexes depends on the stereochemistry of the phosphorus centers and arrangement of –^GN_PS– units in the strands.     

QUANTITATIVE STUDY ON THE PRODUCTION AND KINETICS OF MONONUCLEAR PHAGOCYTES DURING AN ACUTE INFLAMMATORY REACTION

The present communication concerns a quantitative study on the production and kinetics of mononuclear phagocytes during an acute inflammatory response as compared with the steady-state condition. During an acute inflammation induced by an intraperitoneal injection of NBCS, the peritoneal macrophages increase 2.5 times and there is a concomitant threefold increase of the monocytes in the peripheral blood. This increase of the peritoneal macrophages could be caused by a local proliferation of these cells or by the recruitment of monocytes from the circulation. The results of the in vitro and pulse-labeling studies demonstrate that the mitotic activity of the peritoneal macrophages is not increased during the inflammatory response, which indicates that the increase in the number of these cells is not due to local proliferation. Evidence is also presented that the small proportion (maximally 4%) of peritoneal macrophages that synthesize DNA are very recently arrived from the circulation. In agreement with this is the finding that a small number (less than 3%) of the peripheral blood monocytes are capable of synthesizing DNA. Since proof was obtained that the macrophages in the inflammatory peritoneal exudate originate from peripheral blood monocytes and the number of these cells in the circulation was also augmented, an increased formation of monocytes in the bone marrow was expected. Because increased monocyte production could be brought about by an increased number of promonocytes and/or an acceleration of the mitotic activity of the promonocytes, the various parameters of the cell cycle of these cells were determined. In normal mice the DNA-synthesis time of the promonocytes was 11.8 h, the cell cycle time 16.2 h, and the G₁ + G₂ + M phases 4.4 h. During the first 12 h of the inflammatory response a significantly shorter DNA-synthesis time (7.6 h) and cell cycle time (10.8 h) was found. At 24 h, these values approximated those found in normal mice. Next, both the total production and the rate of production of the monocytes were calculated and compared for both conditions. This computation showed that the total production of labeled monocytes during the first 48 h of an acute inflammation was 64% greater than in normal mice. The rate of production, calculated in two ways (i.e., from the data of the total production and also from the data of the cell cycle time together with the total number of promonocytes) complemented each other very well. During the first 12 h of the inflammatory response the production rate was increased 1.5 times and then leveled off, reaching almost the normal rate after 24 h. Furthermore, the excellent agreement between the results of the two methods of calculation for the normal steady state confirmed once more that the promonocyte is the direct precursor cell of the monocyte, giving rise to the two monocytes after each division. The kinetics of the monocytes in the peripheral blood was also altered during the inflammatory response. During the first 48 h, twice the normal number of labeled monocytes went from the bone marrow to the peripheral blood and twice the normal number also left the circulation. Furthermore, at least 70% of this increased number of labeled monocytes leaving the circulation migrated into the inflammatory exudate of the peritoneal cavity, leading to a roughly 11-fold increase of labeled peritoneal macrophages.     

WESTERN EQUINE ENCEPHALOMYELITIS VIRUS IN THE BLOOD OF EXPERIMENTALLY INOCULATED CHICKENS

1. Chickens inoculated subcutaneously with 0.2 cc. of a 10^–2 to 10^–7 dilution of Western equine mouse brain virus had the virus in the blood serum between the 12th and the 48th hour in most instances. The fowls showed no signs of illness. 2. Viremia could be induced regularly in chickens by inoculating subcutaneously the least amount of virus which would produce encephalitis in the mouse when inoculated by the intracerebral route. 3. Even the minimal infecting dose for a chicken led to such multiplication of the virus that it was detectable in the serum in a 10^–4 dilution. Moreover, a minimal infecting dose appeared to result in a longer period of viremia than was produced by a larger dose. 4. Virus has not been found to persist for more than 3 days after inoculation in any organ of the chicken tested for it and usually it did not persist over 2 days. Antibodies were present in the blood within at least 15 days after inoculation. 5. It is concluded that chickens may serve as sources of infection for mosquitoes or other blood-sucking ectoparasites for short periods of time after the infecting bite of a similar invertebrate vector. There is no evidence that the chicken serves as a latent carrier of the virus. 6. No virus could be found in the blood of 2 inoculated calves, and virus has not been demonstrated regularly or with the same case in the blood of horses or of men, as it has in that of chickens. It seems unlikely therefore that large mammals serve frequently as sources for mosquito infection. 7. These experimental data on fowls and mammals correlate well with other epidemiological and laboratory findings, in particular with the feeding preference of the mosquitoes found infected in epidemic areas.     

THE GIX SYSTEM : A CELL SURFACE ALLO-ANTIGEN ASSOCIATED WITH MURINE LEUKEMIA VIRUS; IMPLICATIONS REGARDING CHROMOSOMAL INTEGRATION OF THE VIRAL GENOME

This report concerns a cell surface antigen (G_IX; G = Gross) which exhibits mendelian inheritance but which also appears de novo in cells that become productively infected with MuLV (Gross), the wild-type leukemia virus of the mouse. In normal mice, G_IX is a cell surface allo-antigen confined to lymphoid cells and found in highest amount on thymocytes. Four categories of inbred mouse strains can be distinguished according to how much G_IX antigen is expressed on their thymocytes. G_IX^- strains have none; in the three G_IX⁺ categories, G_IX³, G_IX², and G_IX¹, the amounts of G_IX antigen present (per thymocyte) are approximately in the ratios 3:2:1. A study of segregating populations derived mainly from strain 129 (the prototype G_IX³ strain) and C57BL/6 (the prototype G_IX^- strain) revealed that two unlinked chromosomal genes are required for expression of G_IX on normal lymphoid cells. The phenotype G_IX⁺ is expressed only when both genes are present, as in 129 mice. C57BL/6 carries neither of them. At one locus, expression of G_IX is fully dominant over nonexpression (G_IX fully expressed in heterozygotes). At the second locus, which is linked with H-2 (at a distance of 36.4 ± 2.7 units) in group IX (locus symbol G_IX), expression is semidominant (50% expression of G_IX in heterozygotes); gene order T:H-2:Tla:G_IX. As a rule, when cells of G_IX^- mice or rats become overtly infected with MuLV (Gross), an event which occurs spontaneously in older mice of certain strains and which also commonly accompanies malignant transformation, their phenotype is converted to G_IX⁺. This invites comparison with the emergence of TL⁺ leukemia cells in TL^- mouse strains which has been observed in previous studies and which implies that TL^- → TL⁺ conversion has accompanied leukemic transformation of such cells. So far the only example of G_IX^- → G_IX⁺ conversion taking place without overt MuLV infection is represented by the occurrence of GCSA^-:G_IX⁺ myelomas in BALB/c (GCSA:G_IX^-) mice. Unlike the other Gross cell surface antigen described earlier, GCSA, which is invariably associated with MuLV (Gross) infection and never occurs in its absence, G_IX antigen sometimes occurs independently of productive MuLV infection; for example, thymocytes and some leukemias of 129 mice are GCSA^-:G_IX⁺, and MuLV-producing sarcomas may be GCSA⁺:G_IX^-. The frequent emergence of cells of G_IX⁺ phenotype in all mouse strains implies that the structural gene coding for G_IX antigen is common to all mice. There is precedent for this in the TL system, in which two of the Tla genes in linkage group IX appear to be ubiquitous among mice, but are normally expressed only in strains of mice carrying a second (expression) gene. It is not yet certain whether either of the two segregating genes belongs to the MuLV genome rather than to the cellular genome. This leaves the question whether MuLV may have a chromosomal integration site still debatable. But there is a good prospect that further genetic analysis will provide the answer and so elucidate the special relationship of leukemia viruses to the cells of their natural hosts.     

Regulator of G protein signaling 2 mediates cardiac compensation to pressure overload and antihypertrophic effects of PDE5 inhibition in mice

The heart initially compensates for hypertension-mediated pressure overload by enhancing its contractile force and developing hypertrophy without dilation. G_q protein–coupled receptor pathways become activated and can depress function, leading to cardiac failure. Initial adaptation mechanisms to reduce cardiac damage during such stimulation remain largely unknown. Here we have shown that this initial adaptation requires regulator of G protein signaling 2 (RGS2). Mice lacking RGS2 had a normal basal cardiac phenotype, yet responded rapidly to pressure overload, with increased myocardial G_q signaling, marked cardiac hypertrophy and failure, and early mortality. Swimming exercise, which is not accompanied by G_q activation, induced a normal cardiac response, while Rgs2 deletion in G_αq-overexpressing hearts exacerbated hypertrophy and dilation. In vascular smooth muscle, RGS2 is activated by cGMP-dependent protein kinase (PKG), suppressing G_q-stimulated vascular contraction. In normal mice, but not Rgs2^–/– mice, PKG activation by the chronic inhibition of cGMP-selective phosphodiesterase 5 (PDE5) suppressed maladaptive cardiac hypertrophy, inhibiting G_q-coupled stimuli. Importantly, PKG was similarly activated by PDE5 inhibition in myocardium from both genotypes, but PKG plasma membrane translocation was more transient in Rgs2^–/– myocytes than in controls and was unaffected by PDE5 inhibition. Thus, RGS2 is required for early myocardial compensation to pressure overload and mediates the initial antihypertrophic and cardioprotective effects of PDE5 inhibitors.     

ApoE regulates hematopoietic stem cell proliferation, monocytosis, and monocyte accumulation in atherosclerotic lesions in mice

Leukocytosis is associated with increased cardiovascular disease risk in humans and develops in hypercholesterolemic atherosclerotic animal models. Leukocytosis is associated with the proliferation of hematopoietic stem and multipotential progenitor cells (HSPCs) in mice with deficiencies of the cholesterol efflux–promoting ABC transporters ABCA1 and ABCG1 in BM cells. Here, we have determined the role of endogenous apolipoprotein-mediated cholesterol efflux pathways in these processes. In Apoe^–/– mice fed a chow or Western-type diet, monocytosis and neutrophilia developed in association with the proliferation and expansion of HSPCs in the BM. In contrast, Apoa1^–/– mice showed no monocytosis compared with controls. ApoE was found on the surface of HSPCs, in a proteoglycan-bound pool, where it acted in an ABCA1- and ABCG1-dependent fashion to decrease cell proliferation. Accordingly, competitive BM transplantation experiments showed that ApoE acted cell autonomously to control HSPC proliferation, monocytosis, neutrophilia, and monocyte accumulation in atherosclerotic lesions. Infusion of reconstituted HDL and LXR activator treatment each reduced HSPC proliferation and monocytosis in Apoe^–/– mice. These studies suggest a specific role for proteoglycan-bound ApoE at the surface of HSPCs to promote cholesterol efflux via ABCA1/ABCG1 and decrease cell proliferation, monocytosis, and atherosclerosis. Although endogenous apoA-I was ineffective, pharmacologic approaches to increasing cholesterol efflux suppressed stem cell proliferative responses.     

STUDIES ON THE BACTERIOPHAGE OF D'HERELLE : IV. CONCERNING THE ONENESS OF THE BACTERIOPHAGE.

Lytic filtrates, active against Bacillus dysenteriœ Shiga, Bacillus coli, Bacillus pestis caviœ, and staphylococcus respectively, proved to be differently affected by changes in hydrogen ion concentration. Anti-staphylococcus lysin was the least resistant of the four, showing deterioration in 3 hours at 7°C. beyond the zone of hydrogen ion concentration limited by C_H = 6.3 x 10^–5 and C_H = 1.6 x 10^–9. Under the same conditions, the zone of resistance of anti-coli filtrate lay between C_H = 2.7 x 10^–3 and C_H = 2.5 x 10^–11, and that of anti-Shiga between C_H = 1-7 x 10^–4 and C_H = 1-3 x 10^–11. Anti-pestis caviœ filtrate was most resistant of the four, retaining its full activity in the zone from C_H = 1 x 10^–3 to C_H = 3.5 x 10^–12. The fact that these differences in individual resistance persisted, notwithstanding the repeated passage of lytic filtrates through cultures of bacteria other than those against which they were primarily active, seems to offer evidence in favor of a multiplicity of bacteriophages.